Field of the Invention
The invention relates to a transmission and reception configuration for bi-directional optical data transmission, in particular, through plastic-fiber optical waveguides, having a transmission element and a reception element. Its preferred field of use concerns the bi-directional transmission of data through plastic fibers or polymer fibers (POF fibers).
In the prior art, bi-directional optical transmission paths are produced in full-duplex operation using two separate transmission fibers. For considerations of space and weight and to minimize the number of parts required, however, it is expedient that the data to be transmitted should use only one transmission fiber in both transmission directions. Such a configuration requires transmission and reception configurations for bi-directional optical data transmission that, on one hand, inject the optical power (otherwise referred to as an optical signal or as light) emitted by a transmission element into the transmission fiber and, on the other hand, extract the light emitted by another transmission unit from the transmission fiber, and detect it by using a reception element.
Also in the prior art, bi-directional transmission and reception configurations are used in which the transmission element is disposed in front of the reception element, and the reception diode is covered with a transmission filter that is transparent only for the reception wavelength. Electrical crosstalk between the transmission element and the reception element is, in such a case, substantially prevented by spatial separation of the two elements.
Other prior art bi-directional fiber transmission systems have the light emitted by a laser diode be linearly polarized along an axis. A polarizer in front of the photodiode suppresses optical near-end crosstalk. A disadvantage of such a system is that the reception power is also lost in the polarization direction, so that, on average, only half the reception power is detected. Far-end crosstalk is restricted by not allowing any jack connectors to be installed along the optical path and by reducing the terminal reflection in combination with the fiber attenuation in the backward direction to the extent that a sufficient detection-threshold noise ratio is provided. A disadvantage of the reception element in such a case is that it is not configured for the minimum possible reception power.
It is accordingly an object of the invention to provide a transmission and reception configuration for bi-directional optical data transmission that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that avoids the aforementioned disadvantages of the prior art and, in particular, allows a transmission element (transmitter) and a reception element (receiver) to be disposed next to one another on a substrate.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a transmission and reception configuration for bi-directional optical data transmission, including a substrate, a transmitter for emitting light, disposed on the substrate, a receiver for receiving light, the receiver disposed next to the transmitter on the substrate, a coupling lens for projecting optical received light delivered from an optical waveguide onto the receiver, the coupling lens optically coupled to the receiver and having an edge region, and a micro-lens focusing forward-emitted light of the transmitter and projecting the light onto the edge region, the micro-lens connected to the transmitter, the light being injected from the edge region into the optical waveguide. Preferably, the bi-directional optical data transmission is through plastic-fiber optical waveguides.
Correspondingly, the solution according to the invention is distinguished by the fact that, on one hand, a coupling lens is provided that projects optical light received, delivered through an optical waveguide, onto the receiver. On the other hand, a micro-lens is mounted on the transmitter. The micro-lens focuses forward the emitted light of the transmitter and projects it onto an edge region of the coupling lens, from which it is injected into the optical waveguide.
Hence, the solution according to the invention proposes that the light emitted by the transmitter be projected by using a micro-lens that is located on the transmitter onto an edge region of the coupling lens while the reception power is projected onto the receiver by the coupling lens. As such, the transmission and reception powers are separated despite the fact that the transmission and receivers are disposed next to one another on a substrate. Thus, the solution according to the invention provides a structure of a transmission and reception configuration, in which the transmission and receivers can be disposed next to one another on a substrate.
The configuration permits simpler and more cost-effective manufacture of the transmission and reception configuration.
In accordance with another feature of the invention, the receiver is adjacent the transmitter on the substrate.
In accordance with a further feature of the invention, the receiver has a diameter that is less than the fiber-core diameter of the coupled optical waveguide. The diameter of the receiver, which is, in particular, a photodiode, is preferably in the region of half the fiber-core diameter or less. Such a configuration has the advantage that the photodiode capacitance is small and, in combination with a high transimpedance of a preamplifier, high receiver sensitivity is achieved.
Next to the receiver, the transmitter is mounted a small distance away on the substrate. As such, the receiver and the transmitter preferably lie within the projected cross-sectional area of the fiber core of the coupled optical waveguide. The configuration guarantees a high coupling factor when injecting and extracting transmission and reception powers, respectively, into and from the fiber core.
In accordance with an added feature of the invention, the coupling lens is an aspherical lens, i.e., a lens whose lens surface is aspherically curved. The coupling lens is ground flat on its side facing away from the transmission and receivers, so that an optical waveguide with its end surface can be coupled directly to the coupling lens. The use of an aspherical lens has the advantage that divergent light emerging from the fiber core of the optical waveguide, even in the edge regions, can be projected onto the receiver.
In accordance with an additional feature of the invention, the micro-lens disposed on the transmitter has an aspherical curvature so that the emitted light can be projected onto a limited edge region of the preferably aspherical coupling lens.
In accordance with yet another feature of the invention, the coupling lens is bi-focally configured, with the coupling lens forming a second lens in the injection region of the optical power of the transmitter. The configuration maximizes the injection of the transmission power into the fiber. The coupling lens is correspondingly constructed such that it primarily focuses the optical received light onto the receiver and, in a small edge region, injects the transmission power of the transmitter maximally into the fiber.
In accordance with yet a further feature of the invention, the coupling lens forms a short waveguide appendage that extends in the direction of or towards the transmitter. The waveguide appendage is preferably provided with a converging lens on its end. Because of the short distance between the transmitter with the micro-lens and the waveguide appendage, coupling losses can be kept extremely low in such an embodiment.
In accordance with yet an added feature of the invention, there is provided a transmission filter disposed at the receiver, the transmission filter being non-transparent to light of a given wavelength. In other words, the transmission filter can be disposed upstream of the receiver with respect to a receiving direction of the receiver or in front of the receiver.
If different wavelengths are used for the bi-directional optical data transmission, undesired reflection of the transmission power from the end surfaces of the lenses and from the end surface of the optical fiber will preferably be kept away from the receiver by a color transmission filter, which is optically transparent with respect to the reception wavelength. The transmission filter is, in such a case, disposed over the receiver. By using a transmission filter, noise signals can be suppressed to the extent that there is no effect on the bit error rate and, therefore, the receiver sensitivity of the receiver.
In accordance with yet an additional feature of the invention, preferably, the transmission filter is additionally configured as a converging lens so that received radiation can be projected even better onto the receiver.
In accordance with again another feature of the invention, the light emitted from the transmitter is one of the group consisting of green light and red light, the light received by the receiver is one of the group consisting of red light and green light, and the transmission filter is one of the group consisting of a red filter and a green filter.
If the transmission and reception configuration uses light signals of the same wavelength for the bi-directional data transmission, then it is necessary to ensure that no, or only very little, direct light or scattered light of the transmitter crosstalks to the receiver. To that end, in accordance with again a further feature of the invention, an attenuation filter, which is intended to keep the light of the transmission diode away from the receiver, is preferably assigned to or associated with the receiver.
In accordance with again an added feature of the invention, the transmitter transmits an optical signal including light at a given wavelength, the receiver receives light at the given wavelength, and the attenuation filter protects the receiver from the light emitted from the transmitter.
In accordance with again an additional feature of the invention, the attenuation filter is preferably configured as a ring, which is non-transparent for the transmission wavelength and is disposed around the receiver. The ring preferably extends over a particular height in the direction of the coupling lens and, hence, constitutes, so to speak, a protective wall around the receiver. The configuration prevents, in particular, direct lateral crosstalk from the transmitter to the receiver.
In accordance with still another feature of the invention, the ring extends from the coupling lens.
In accordance with still a further feature of the invention, the ring extends towards the receiver.
Provision may also be made for the ring to be thickened in subregions, in particular, in order to suppress reflected powers from the front reflection or from the end surface of the aspherical coupling lens.
The ring that is non-transparent for the transmission wavelength is preferably connected to a transparent transmission filter that is disposed on the receiver. The transparent filter is preferably configured as a lens that is located in front of the receiver.
Directly next to the receiver, in accordance with a concomitant feature of the invention, a second receiver, preferably having the same construction and that is covered with an optically non-transparent layer, is disposed on the substrate or formed therein. Preferably, the second receiver is disposed directly next to the receiver on the substrate, the receiver and the second receiver each transmit output signals, and an evaluation circuit is connected to the receiver and to the second receiver, the evaluation circuit filtering out noise signals by taking a difference between respective ones of the output signals. In such a case, an evaluation circuit that very greatly reduces, or ideally eliminates, the electrical crosstalk by taking the difference between the respective signals, is assigned to the two receivers. The basis of the differential evaluation is that the second receiver exclusively detects noise radiation.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a transmission and reception configuration for bi-directional optical data transmission, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.